This application claims priority of Italian Application No. TO2000A 000918 filed Oct. 3, 2000 hereby incorporated herein by reference.
The present invention relates to a device for controlling the flow of a high-pressure pump in a common-rail fuel injection system of an internal combustion engine, wherein the high-pressure pump is a constant-displacement type supplied with fuel by a low-pressure, variable-delivery, variable-pressure pump.
As is known, in modern internal combustion engines, each injector is supplied with high-pressure fuel by a common header or so-called xe2x80x9ccommon railxe2x80x9d, which is supplied by a high-pressure, normally piston, pump in turn supplied with fuel from the fuel tank by a low-pressure pump.
The low-pressure pump normally supplies fuel at a pressure of around a few bars, while the fuel in the rail may reach pressures in the region of 1500 bars. The high-pressure pump is normally operated by the internal combustion engine drive shaft via a drive belt or similar (gears), whereas the low-pressure pump is operated by a direct-current electric motor or equivalent (brushless motors) of its own, and so defines a motor-drive pump.
On account of the varying operating load of the internal combustion engine, the two pumps must be designed to guarantee the necessary fuel supply to the injectors in the worst possible conditionsxe2x80x94i.e. with the engine at full load and/or high speed with fuel leakagexe2x80x94and with any external temperature and any fuel temperature in the tank. The surplus fuel supplied by each pump is fed back into the tank via respective pressure control valves and drain conduits.
The high-pressure pump therefore draws the maximum amount of energy at all times, which must be supplied by the internal combustion engine. Moreover, due to heating of the fuel by the heat dissipated as a result of the difference of pressure across the pressure regulating valve of the pump, the fuel drained into the tank tends to heat the fuel to be pumped, which therefore becomes more fluid, thus increasing fuel leakage, e.g. between the pistons and cylinders, and so reducing the volumetric efficiency of the pump.
Various types of devices are known for controlling the flow of common-rail injection system high-pressure pumps. In one known type, flow is regulated by varying the piston, e.g. suction, stroke to vary displacement of the pump mechanically. The mechanisms by which the stroke is varied, however, are highly complex and expensive to produce; and, during the compression stroke, the reduction in the suction stroke of the pistons causes the drive cam to strike the pistons, thus resulting in frequent malfunctioning or damage to the pump.
Devices are also known for controlling the flow of constant-displacement high-pressure pumps, and which provide for regulating the fuel supply to the pump. In one known type, this is done by means of a regulating valve fitted to the delivery side of the low-pressure pump to adjust the fuel flow section.
Known control devices of this sort have the drawback of being expensive to produce and unreliable; and both the diaphragms and the valve involve additional expense in terms of both manufacture and in-service checks. Moreover, particularly at idling engine speed, such devices fail to ensure equal fuel supply to all the high-pressure pump pistons, thus resulting in unbalanced operation and rapid wear of the pump.
It is an object of the present invention to provide a device for controlling the flow of a high-pressure pump, which is straightforward in design, cheap to produce, ensures a high degree of efficiency and reliability, and provides for eliminating the aforementioned drawbacks typically associated with known devices.
According to the present invention, there is provided a device for controlling the flow of a high-pressure pump in a common-rail fuel injection system of an internal combustion engine, wherein said high-pressure pump is a constant-displacement type and is supplied with fuel by a low-pressure, variable-delivery, variable-pressure pump; characterized by comprising a choke on the suction side of said high-pressure pump; and means for controlling said low-pressure pump to vary the fuel pressure upstream from said choke between a maximum predetermined value and a minimum predetermined value, so as to regulate fuel intake by said high-pressure pump within a predetermined range.
More specifically, said low-pressure pump is a motor-driven pump, and said means comprise an electronic control unit for receiving signals indicating the operating conditions of the engine; said control unit controlling said motor-driven pump as a function of said signals.